Interpolation and Beth Definability over the Minimal Logic

Extensions of the Johansson minimal logic J are investigated. It is proved that the weak interpolation property WIP is decidable over J. Well-composed logics with the Graig interpolation property CIP, restricted interpolation property IPR and projective Beth property PBP are fully described. It is proved that there are only finitely many well-composed logics with CIP, IPR or PBP; for any well-composed logic PBP is equivalent to IPR, and all the properties CIP, IPR and PBP are decidable on the class of well-composed logics..